A passive optical network (PON) is one system for providing network access over “the last mile.” A PON is a point-to-multipoint network comprised of an optical line terminal (OLT) at a central office (CO), an optical distribution network (ODN), and a plurality of optical network units (ONUs) at the user premises. PONs may also comprise remote nodes (RNs) located between the OLTs and ONUs, for instance at the end of a road where multiple users reside.
In recent years, time-division multiplexing (TDM) PONs, such as Gigabit PONS (GPONs) and Ethernet PONs (EPONs), have been deployed worldwide for multimedia applications. In TDM PONs, the total capacity is shared among multiple users using a time-division multiple access (TDMA) scheme, so the average bandwidth for each user may be limited to below 100 megabits per second (Mbps).
Wavelength-division multiplexing (WDM) PONs are considered a very promising solution for future broadband access services. WDM PONs can provide high-speed links with dedicated bandwidth up to 10 gigabits per second (Gbps). In a WDM PON, each ONU is served by a dedicated wavelength channel to communicate with the central office or the OLT.
One type of WDM is dense WDM (DWDM). DWDM may combine along a single optical fiber multiple optical signals at various wavelengths. DWDM PONs may provide additional bandwidth, but may also require the use of tunable lasers, which may refer to lasers that may be tuned to emit laser beams at specific wavelengths. Those specific wavelengths may be in the C band, which may refer to wavelengths in the range of 1,528 nanometers (nm) to 1,565 nm. It is therefore desirable to design such tunable lasers in a high-performance manner.